Synthetic baling and tying twines



April 25, 1967 w. L. CARRANZA SYNTHETIC BALING AND TYING TWINES FiledMarch 9, 1964 INVENTOR M4 4 09/") Z wee/9W2 y ATTORNEYS ydzwy UnitedStates Patent 3,315,454 SYNTHETIC BALING AND TYING TWINES William L.Carranza, 4401 SW. 13th St., Miami, Fla. 33134 Filed Mar. 9, 1964, Ser.No. 350,583 7 Claims. (Cl. 57140) The present invention relates to twineand more particularly to a synthetic twine suitable for use in automaticknot tying machines such as hay balers and the like. The twine iscomposed of filaments of synthetic high polymer, preferably polyethyleneor polypropylene, which have been impregnated with a gas-for exampleair-to alter their properties and overcome their natural unsuitabilityfor automatic knot tying.

In agriculture and many businesses, it has now been found uneconomicaland undesirable to tie packages by hand. Large packages require severalpeople working together with resultant high labor costs. Even in thecase of smaller packages, binding with twine and tying of knots is slow.Unless experienced persons are employed, the twine may not be wrappedproperly and the knots will not be consistently tight.

Consequently, a Wide variety of machine have been developed whichautomatically wrap a package with twine, cut the twine and tie a knot.Perhaps the most commonly known are the hay balers which generally tiesingle loop knots. Tying machines are used to tie newspapers, currency,bundles of mail, catalogs, magazines, paper products, tobacco products,meats, laundry, textile goods, leather goods such as soles and insoles,nursery stock such as seedling plants, bushes and small trees, coils ofwire and hundreds of other kinds of hard and soft packages. The tyingmachines often are capable of adjusting, sometimes automatically, todifferent sizes of packages. They may tie several types of knots, singleloop, double loop, bow, etc., and can wrap and tie packages at the rateof 15 to per minute. Thus, the terms tying twine and baling twine asused herein is intended to comprehend twines useful in all of the abovetypes of machine.

For the most part, these machines use twines composed of natural fibers,principally cotton, jute and sisal, a particular twine being selected ona basis of strength and other requirements. For example, cotton twinestend to be soft although not as strong as sisal and would be used whenthe articles being tied are soft. However, these natural fibers for themost part are available only in certain parts of the world and theirsupply and price depend on crop conditions, availability of shipping andother factors. Like all natural products, their quality is not uniform.Consequently, there is a genuine need for a twine composed of syntheticmaterial.

Considerable effort has been expended in the search for a suitablesynthetic twine. Many types of synthetic fibers have been tested.However, they have been found generally unsatisfactory because theycannot be tied in conventional knots by the above machines. Because ofslippery surfaces and other properties, the knots do not remain tied andthe twine slips loose. Consequently, synthetic twines have not beenwidely accepted.

In a previous application, I have described a solution to the problem inwhich the twine is polyethylene or polypropylene which carries anadhesive and abrasive to increase friction in the appropriate amount andotherwise adapt the twine to automatic knot tying. While that twine isfully satisfactory, I have continued my research in an effort to furtherreduce costs.

In accordance with the present invention, a twine is made from asynthetic resin, preferably from a polyolefin and more preferably frompolyethylene or polypropylene,

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which has been impregnated with a controlled amount of gas. In general,gas impregnation may have a tendency to reduce the tensile strength ofplastics, and increase their elasticity, but I have found that bylimiting the amount of gas to about 35% by volume, sufiicient tensilestrength remains while the properties of the twine are adapted toautomatic knot tying machines.

Surprisingly, the new twine is suited for mechanical knotting eventhough its surface has not been treated to alter frictioncharacteristics. The reason for such behavior is not completelyunderstood, but it is believed to be related at least in part to changesin the flexibility and compressibility of the twine. Thus, while knotslippage of synthetic twine has always been thought to be caused by therelatively slippery surface of the plastics, it has been found that itis at least partially the result of relative inflexibility andincompressibility.

The invention is illustrated in the drawing in which FIGURE 1 shows inperspective one form of a twine comprising a plurality of filamentsembodying the principles of the invention; and

FIGURE 2 is an enlarged view of a portion of one filament of the twineof FIGURE 1 viewed from the end thereof.

The synthetic resins preferred are polyethylene and polypropylene. Thepolyethylene used may be a so-called high density polyethylene, such asis described in Peters United States Patent No. 2,692,259 or is obtainedby the so-called Ziegler process. These high-density polyethylenes haveextremely good tensile strength. Other types of polyethylene may beused, provided a sufiicient number of strands of suitable size are used,to give a satisfactory over-all tensile strength. The polypropylenesinclude those developed by Natta which were described in the Journal ofthe American Chemical Society, vol. 77, pages 1708-10 (1955) and havemore recently been described in greater detail. These and other suitablethermoplastic polyolefins may be treated with carbon black, anti-oxidantto increase their resistance to light or atmospheric agents, or smallamounts of additives which alter somewhat the surface 'frictioncoefficient, preferably before the thermoplastic is spun into filaments.It will be understood that the terms polyethylene and polypropyleneinclude also copolymers with each other or different monomers which aresimilar to polyethylene and polypropylene and are suitable for twineexcept for the above knot tying difficulties.

The polymer may be impregnated with air or another inert gas prior to orafter extrusion or other shaping into the form of filaments, preferablyin such manner as to provide, in addition to dissolved gas, small,discrete, connected or isolated vesicles of gas which are substantiallyuniformly distributed throughout. Suitable methods for making suchfilaments already are well known to those skilled in the art and form nopart of the present invention. However, by way of illustration, suchmethods may include injecting air or other gas into the polymer while itis in an extruder prior to extrusion as filaments. It also is possibleto impregnate the polymer under pressure with a volatile liquid which isgaseous at normal temperatures and allow the liquid to evaporate, say,when the polymer is heated to a temperature where it is partiallysoftened, or relaxed. In another embodiment, the gas may be supplied bychemical agents which release gas at elevated temperatures.

The amount of gas used should be the maximum. It will vary somewhatamong various types and grades of material but, in general, the upperlimit is about 3035% There is no actual lower limit, since as much aspossible should be used, but at least about 5%, preferably at least 10%,should be in the plastic to take advantage of the.

lferent sizes and to use these together.

principles of the invention. Any substance, which is a gas at ordinarytemperatures (above about 40) may be used, the selection depending onthe method of introducing it. For example, air, Freons, carbon dioxide,nitrogen, etc. are suitable. The substance should not, of course, attackthe polymer.

The twine is composed of a plurality of such filaments which may betwisted together. It will be appreciated that the term filaments is usedto refer to single elongated bodies of plastic. This term sometimes isused to specify a single integral continuous body of plastic, i.e., amonofilament, as distinguished from threads which have been formed byspinning staple fibers. However, no such limitation is intended sincespun filaments and monofilaments are equally useful in the practice oftheinvention.

In general, the size and structure of the twine will vary in accordancewith the kind of tying for which it is intended. However, overall sizewill be in the range about 6,000 to 28,000 deniers. Tying twins will bein the range 6,000-18,000 deniers and baling twines in the range 19,000to 28,000 deniers. In certain cases, the baling twines may be used forheavy tying machines, but thick twine of this type will nevertheless bedesignated baling twine for the purpose of classification. Theindividual filaments may vary in size from about 65 to 950 deniers,

i.e., about 4 to mils, and they may be of thesame or different sizes.The filaments may be round, square or have any other round or non-roundshape.

The sizes of'the filaments and twine Will determine the 7 number offilaments. That is, larger numbers offilaments must be used as theirdiameter is decreased. The total number of filaments should give atensilestrength of 12.5 lbs. or more for tying twines and at least 180lbs. for

baling twines. The filaments may be laid together and, if desired,twisted. In most cases, twisted twines are preferred, but untwistedtwines are suitable for some purposes. When the twine is twisted, thedegree of twist may vary. However, usually it will not exceed ten turnsper inch and preferably it will be less than five turns per inch. Verysatisfactory twines have a twist of /2 to '-/3 turn per inch.

In some cases, it may be desirable to pre-assemble the filaments intoseveral small bundles of the same or dif- The individual bundles may betwisted in the same or opposite directions before they are twistedtogether.

The individual filaments and/ or the twine may be subject to anystretching, shrinking, heating or cooling treatment which does notremove or undesirably alter the gas composition and distribution. Forexample, the twisted twine may be heat set under sufficient tension toprevent shrinkage, or stretched up to 10%. However, excessive I heatingto near or above the softening point may lead to an undesirable lossofthe gas or to the equally unsatisfactory accumulation of gas in a fewlarge bubbles of irregular size. A mild heat setting of twisted twinesis desirable as it tends'to fix the twist and compact the structure.

The finished twine may, if desired, be coated with adhe- 4 sive andabrasive in the manner described, but this is regarded as unncessary formost uses.

The following example illustrates the invention.

Example A twine was made by twisting together forty polypropylenefilaments at about /3 turns per inch. Each filament was about 9 milsdiameter blown with sufficient air to increase its diameter to about1l.5l2 mils. The twine, which was about 23,000 denier in diameter, washeat set mode of operation without departing from the true scope.

thereof, as defined in the claims.

What is claimed is:

1. Synthetic twine suitable for forming non-slippingknots in baling,tying and other automatic knot tying machines which comprises aplurality of filaments of a thermoplastic synthetic resin selected fromthe group consisting of polyethylene and polypropylene, said filamentshaving a diameter of about 65 to 950 deniers and containing dispersedtherein a substance which is a gas at ordi 1 nary temperatures in anamount up to about 35% by' A volume based on the volume of the resin,said twine hav- 0 ing a denier in the range about 6,000 to 28,000.

2. Synthetic twine as set forth in claim 1 in which the twine istwisted.

3. Synthetic twine as set forth in claim 2 in which the degree of twistis less thanten turns per inch.

4. Synthetic twine assetforth in claim 3 in which the degree of twist isless than five turns per inch.

5. Synthetic twine as set forth in claim 1 in which the amount of saidgas is about 5% to 35% by volume based 7 on the volume of the resin.

6. Synthetic twine as set forth in claim 5 in which the amount of saidgas is about 10% to 30% by volume based on the volume of resin.

7. Synthetic twine as set forth in resin is polypropylene.

References Cited by the Examiner UNITED STATES PATENTS MERVIN STEIN,Primary Examiner.

claim 1 in which said

1. SYNTHETIC TWINE SUITABLE FOR FORMING NON-SLIPPING KNOTS IN BALING,TYING AND OTHER AUTOMATIC KNOT TYING MACHINES WHICH COMPRISES APLURALITY OF FILAMENTS OF A THERMOPLASTIC SYNTHETIC RESIN SELECTED FROMTHE GROUP CONSISTING OF POLYETHYLENE AND POLYPROPYLENE, SAID FILAMENTSHAVING A DIAMETER OF ABOUT 65 TO 950 DENIERS AND CONTAINING DISPERSEDTHEREIN A SUBSTANCE WHICH IS A GAS AT ORDINARY TEMPERATURES IN AN AMOUNTUP TO ABOUT 35% BY VOLUME BASED ON THE VOLUME OF THE RESIN, SAID TWINEHAVING A DENIER IN THE RANGE ABOUT 6,000 TO 28,000.